In the 21st century, nanotechnology is widely used. Nanometer is the unit of length. If one meter is 10 ^ 9 nanometers, how many nanometers is 55 meters in scientific notation?

Analysis:
1 m = 10 ^ 9 nm, then:
55m = 55 × 10 ^ 9nm = 5.5 × 10 ^ 10nm

Nanometer is the unit of length. How many cubic nanometers is the cuboid with a length of 5 meters, a width of 4 meters and a height of 3 meters?

3*4*5=60M3,M=1*10^9NM
So the volume is 6 * 10 ^ 28nm

Given the complex number Z1 = cos α + asin α, Z2 = cos β + isin β, | z1-z2 | = (2 √ 5) / 5, find cos (α + β)
Where did I go?

Cos (α - β), right?
|z1-z2|=|cosα-cosβ+i(sinα-sinβ)|=2/√5
So (COS α - cos β) ^ 2 + (sin α - sin β) ^ 2 = 4 / 5
2-2cos (α - β) = 4 / 5
cos(α-β)=3/5

If we know that Z1 = cos α + isin α, Z2 = cos β + isin β, then the real parts of Z1 and Z2 are?
What is the real part of Z1 + Z2?

Complex Z1 = cos α + isin α,
The real part is cosa and the imaginary part is isin α,
z2=cosβ+isinβ,
The real part is cos β and the imaginary part is isin β
The real part of Z 1 + Z 2 is cosa + cos β

If the solution set of the inequality ax square + BX + C > 0 is (- 2,3), find the inequality CX square + ax-b

In the quadratic equation AX ^ 2 + BX + C = 0 (a ≠ 0 and △ = B ^ 2-4ac > 0), if two roots are X1 and X2, then
　　X1+X2= -b/a
　　X1*X2=c/a
The test point of this question
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It can be seen from the meaning of the title:
In ax ^ 2 + BX + C = 0 (a ≠ 0 and △ = B ^ 2-4ac > 0), if two roots are X1 and X2, then:
-b/a =1
c/a =-6
c>0
a0
CX ^ 2 + ax-b = 0, because △ = a ^ 2 + 4bc > 0, the two roots are X1 and X2, respectively
x1+x2=-a/c=1/6
x1*x2=-b/c=a/c=-1/6
Explanation
X1=1/2
X2=-1/3
Because C > 0
So CX ^ 2 + ax-b

Can you tell me the name of the school which you visited

You visited the school
The antecedent is used as an object in a clause, not as an adverbial

The fence around a semicircle flowerbed is 25.7m long. How much area does the flowerbed occupy

25.7 = R + 2R
S = R ^ 2 / 2
S=39.25

Exact (adjective)

Excited (of a person)
Exciting (to describe something)
For example:
He is excited at the exciting news.
He was very excited about the exciting news

Using cosine theorem to prove that the sum of squares of two diagonals of parallelogram is equal to the sum of squares of four sides
Such as the title

Suppose that the parallelogram ABCD, then ∠ a = 180 °～ B, ab = CD, ad = BC
In △ abd, BD & # 178; = AB & # 178; + AD & # 178; - 2Ab * ad * cosa
In △ ABC, AC & # 178; = AB & # 178; + BC & # 178; - 2Ab * BC * CoSb = CD & # 178; + BC & # 178; - 2Ab * adcos (180 ° - a) = CD & # 178; + BC & # 178; + 2Ab * ad * cosa
By adding the two formulas, AC & # 178; + BD & # 178; = AB & # 178; + AD & # 178; + CD & # 178; + BC & # 178;
That is, the sum of the squares of the two diagonals of a parallelogram is equal to the sum of the squares of the four sides

The difference and usage of past tense and past participle in English

The past tense of verbs can be divided into regular verbs and irregular verbs
(1) In general, add - ed at the end of the verb
worked played wanted acted
(2) End the verb with a silent - E and add - D at the end of the verb
lived moved decided declined hoped judged raised wiped
(3) For verbs ending with the consonant + y, change - y to - I and then add - ed
studied tried copied justified cried carried embodied emptied
(4) For stressed closed syllable verbs ending with a consonant, double write the final consonant and add - ed
stopped begged fretted dragged dropped planned dotted dripped
(5) Note: the past tense of irregular verbs does not change regularly and should be memorized more
Go - went, make - made, get - got, buy - bone, come - cam, fly - fly, is / AM was, are were, see - saw, bring - brown, do - did, teach - thought, think - thought, are were, say - said, sit - Sat. read - read, spend - spend. (part)
1. Regular verbs: the rules of forming the past participle of regular verbs are the same as those of forming the past tense of regular verbs
(1) A general verb with "Ed" at the end
work---worked---worked ,visit---visited---visited
(2) For verbs ending with "e", just add "d" at the end of the word
live---lived---lived ,
(3) For verbs ending with "consonant + Y", change "Y" into "I" and add "Ed"
study---studied---studied ,cry---cried---cried ,
(4) At the end of the closed syllable, there is only one consonant at the end
stop---stopped---stopped , drop---dropped--dropped

In the 21st century, nanotechnology is widely used. Nanometer is the unit of length. If one meter is 10 ^ 9 nanometers, how many nanometers is 55 meters in scientific notation?